<?php
/**
 * CDbCache class file
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @link http://www.yiiframework.com/
 * @copyright Copyright &copy; 2008-2011 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

/**
 * CDbCache implements a cache application component by storing cached data in a database.
 *
 * CDbCache stores cache data in a DB table named {@link cacheTableName}.
 * If the table does not exist, it will be automatically created.
 * By setting {@link autoCreateCacheTable} to false, you can also manually create the DB table.
 *
 * CDbCache relies on {@link http://www.php.net/manual/en/ref.pdo.php PDO} to access database.
 * By default, it will use a SQLite3 database under the application runtime directory.
 * You can also specify {@link connectionID} so that it makes use of
 * a DB application component to access database.
 *
 * See {@link CCache} manual for common cache operations that are supported by CDbCache.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @version $Id: CDbCache.php 3198 2011-04-30 21:14:17Z qiang.xue $
 * @package system.caching
 * @since 1.0
 */
class CDbCache extends CCache
{
    /**
     * @var string the ID of the {@link CDbConnection} application component. If not set,
     * a SQLite3 database will be automatically created and used. The SQLite database file
     * is <code>protected/runtime/cache-YiiVersion.db</code>.
     */
    public $connectionID;
    /**
     * @var string name of the DB table to store cache content. Defaults to 'YiiCache'.
     * Note, if {@link autoCreateCacheTable} is false and you want to create the DB table
     * manually by yourself, you need to make sure the DB table is of the following structure:
     * <pre>
     * (id CHAR(128) PRIMARY KEY, expire INTEGER, value BLOB)
     * </pre>
     * Note, some DBMS might not support BLOB type. In this case, replace 'BLOB' with a suitable
     * binary data type (e.g. LONGBLOB in MySQL, BYTEA in PostgreSQL.)
     * @see autoCreateCacheTable
     */
    public $cacheTableName='YiiCache';
    /**
     * @var boolean whether the cache DB table should be created automatically if it does not exist. Defaults to true.
     * If you already have the table created, it is recommended you set this property to be false to improve performance.
     * @see cacheTableName
     */
    public $autoCreateCacheTable=true;
    /**
     * @var CDbConnection the DB connection instance
     */
    private $_db;
    private $_gcProbability=100;
    private $_gced=false;

    /**
     * Initializes this application component.
     *
     * This method is required by the {@link IApplicationComponent} interface.
     * It ensures the existence of the cache DB table.
     * It also removes expired data items from the cache.
     */
    public function init()
    {
        parent::init();

        $db=$this->getDbConnection();
        $db->setActive(true);
        if($this->autoCreateCacheTable)
        {
            $sql="DELETE FROM {$this->cacheTableName} WHERE expire>0 AND expire<".time();
            try
            {
                $db->createCommand($sql)->execute();
            }
            catch(Exception $e)
            {
                $this->createCacheTable($db,$this->cacheTableName);
            }
        }
    }

    /**
     * @return integer the probability (parts per million) that garbage collection (GC) should be performed
     * when storing a piece of data in the cache. Defaults to 100, meaning 0.01% chance.
     * @since 1.0.9
     */
    public function getGCProbability()
    {
        return $this->_gcProbability;
    }

    /**
     * @param integer $value the probability (parts per million) that garbage collection (GC) should be performed
     * when storing a piece of data in the cache. Defaults to 100, meaning 0.01% chance.
     * This number should be between 0 and 1000000. A value 0 meaning no GC will be performed at all.
     * @since 1.0.9
     */
    public function setGCProbability($value)
    {
        $value=(int)$value;
        if($value<0)
        $value=0;
        if($value>1000000)
        $value=1000000;
        $this->_gcProbability=$value;
    }

    /**
     * Creates the cache DB table.
     * @param CDbConnection $db the database connection
     * @param string $tableName the name of the table to be created
     */
    protected function createCacheTable($db,$tableName)
    {
        $driver=$db->getDriverName();
        if($driver==='mysql')
        $blob='LONGBLOB';
        else if($driver==='pgsql')
        $blob='BYTEA';
        else
        $blob='BLOB';
        $sql=<<<EOD
CREATE TABLE $tableName
(
	id CHAR(128) PRIMARY KEY,
	expire INTEGER,
	value $blob
)
EOD;
        $db->createCommand($sql)->execute();
    }

    /**
     * @return CDbConnection the DB connection instance
     * @throws CException if {@link connectionID} does not point to a valid application component.
     */
    public function getDbConnection()
    {
        if($this->_db!==null)
        return $this->_db;
        else if(($id=$this->connectionID)!==null)
        {
            if(($this->_db=Yii::app()->getComponent($id)) instanceof CDbConnection)
            return $this->_db;
            else
            throw new CException(Yii::t('yii','CDbCache.connectionID "{id}" is invalid. Please make sure it refers to the ID of a CDbConnection application component.',
            array('{id}'=>$id)));
        }
        else
        {
            $dbFile=Yii::app()->getRuntimePath().DIRECTORY_SEPARATOR.'cache-'.Yii::getVersion().'.db';
            return $this->_db=new CDbConnection('sqlite:'.$dbFile);
        }
    }

    /**
     * Sets the DB connection used by the cache component.
     * @param CDbConnection $value the DB connection instance
     * @since 1.1.5
     */
    public function setDbConnection($value)
    {
        $this->_db=$value;
    }

    /**
     * Retrieves a value from cache with a specified key.
     * This is the implementation of the method declared in the parent class.
     * @param string $key a unique key identifying the cached value
     * @return string the value stored in cache, false if the value is not in the cache or expired.
     */
    protected function getValue($key)
    {
        $time=time();
        $sql="SELECT value FROM {$this->cacheTableName} WHERE id='$key' AND (expire=0 OR expire>$time)";
        $db=$this->getDbConnection();
        if($db->queryCachingDuration>0)
        {
            $duration=$db->queryCachingDuration;
            $db->queryCachingDuration=0;
            $result=$db->createCommand($sql)->queryScalar();
            $db->queryCachingDuration=$duration;
            return $result;
        }
        else
        return $db->createCommand($sql)->queryScalar();
    }

    /**
     * Retrieves multiple values from cache with the specified keys.
     * @param array $keys a list of keys identifying the cached values
     * @return array a list of cached values indexed by the keys
     * @since 1.0.8
     */
    protected function getValues($keys)
    {
        if(empty($keys))
        return array();

        $ids=implode("','",$keys);
        $time=time();
        $sql="SELECT id, value FROM {$this->cacheTableName} WHERE id IN ('$ids') AND (expire=0 OR expire>$time)";

        $db=$this->getDbConnection();
        if($db->queryCachingDuration>0)
        {
            $duration=$db->queryCachingDuration;
            $db->queryCachingDuration=0;
            $rows=$db->createCommand($sql)->queryAll();
            $db->queryCachingDuration=$duration;
        }
        else
        $rows=$db->createCommand($sql)->queryAll();

        $results=array();
        foreach($keys as $key)
        $results[$key]=false;
        foreach($rows as $row)
        $results[$row['id']]=$results[$row['value']];
        return $results;
    }

    /**
     * Stores a value identified by a key in cache.
     * This is the implementation of the method declared in the parent class.
     *
     * @param string $key the key identifying the value to be cached
     * @param string $value the value to be cached
     * @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
     * @return boolean true if the value is successfully stored into cache, false otherwise
     */
    protected function setValue($key,$value,$expire)
    {
        $this->deleteValue($key);
        return $this->addValue($key,$value,$expire);
    }

    /**
     * Stores a value identified by a key into cache if the cache does not contain this key.
     * This is the implementation of the method declared in the parent class.
     *
     * @param string $key the key identifying the value to be cached
     * @param string $value the value to be cached
     * @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
     * @return boolean true if the value is successfully stored into cache, false otherwise
     */
    protected function addValue($key,$value,$expire)
    {
        if(!$this->_gced && mt_rand(0,1000000)<$this->_gcProbability)
        {
            $this->gc();
            $this->_gced=true;
        }

        if($expire>0)
        $expire+=time();
        else
        $expire=0;
        $sql="INSERT INTO {$this->cacheTableName} (id,expire,value) VALUES ('$key',$expire,:value)";
        try
        {
            $command=$this->getDbConnection()->createCommand($sql);
            $command->bindValue(':value',$value,PDO::PARAM_LOB);
            $command->execute();
            return true;
        }
        catch(Exception $e)
        {
            return false;
        }
    }

    /**
     * Deletes a value with the specified key from cache
     * This is the implementation of the method declared in the parent class.
     * @param string $key the key of the value to be deleted
     * @return boolean if no error happens during deletion
     */
    protected function deleteValue($key)
    {
        $sql="DELETE FROM {$this->cacheTableName} WHERE id='$key'";
        $this->getDbConnection()->createCommand($sql)->execute();
        return true;
    }

    /**
     * Removes the expired data values.
     * @since 1.0.11
     */
    protected function gc()
    {
        $this->getDbConnection()->createCommand("DELETE FROM {$this->cacheTableName} WHERE expire>0 AND expire<".time())->execute();
    }

    /**
     * Deletes all values from cache.
     * This is the implementation of the method declared in the parent class.
     * @return boolean whether the flush operation was successful.
     * @since 1.1.5
     */
    protected function flushValues()
    {
        $this->getDbConnection()->createCommand("DELETE FROM {$this->cacheTableName}")->execute();
        return true;
    }
}
